Motor vehicles, such as, for example, hybrid vehicles use multiple propulsion systems to provide motive power. This most commonly refers to gasoline-electric hybrid vehicles, which use gasoline (petrol) to power internal-combustion engines (ICEs), and electric batteries to power electric motors. These hybrid vehicles recharge their batteries by capturing kinetic energy via regenerative braking. When cruising or idling, some of the output of the combustion engine is fed to a generator (merely the electric motor(s) running in generator mode), which produces electricity to charge the batteries. This contrasts with all-electric cars which use batteries charged by an external source such as the grid, or a range extending trailer. Nearly all hybrid vehicles still require gasoline as their sole fuel source though diesel and other fuels such as ethanol or plant based oils have also seen occasional use.
Batteries and cells are important energy storage devices well known in the art. The batteries and cells typically comprise electrodes and an ion conducting electrolyte positioned therebetween. Battery packs that contain lithium ion batteries are increasingly popular with automotive applications and various commercial electronic devices because they are rechargeable and have no memory effect. Operating the lithium ion battery at an optimal operating temperature is very important to the batteries performance and lifespan.
Due to the characteristics of the lithium ion batteries, the battery pack is typically specified to operate-within an approximate ambient temperature range of −30° C. to 60° C. However, even when operating within this temperature range, the battery pack may begin to lose its capacity or ability to charge or discharge should it remain at the extremes for long periods of time. Nonetheless, it may be unavoidable that the lithium ion battery be used where the ambient temperature falls outside the temperature range.
Alluding to the above, significant temperature variances can occur from one cell to the next, which is detrimental to performance of the battery pack. To promote long life of the entire battery pack, the cells must be below a desired threshold temperature. To promote pack performance, the differential temperature between the cells in the battery pack should be minimized. However, depending on the thermal path to ambient, different cells will reach different temperatures. Further, for the same reasons, different cells reach different temperatures during the charging process. Accordingly, if one cell is at an increased temperature with respect to the other cells, its charge or discharge efficiency will be different, and, therefore, it may charge or discharge faster than the other cells. This will lead to decline in the performance of the entire pack.
The art is replete with various designs of the battery packs with cooling and packaging systems. The U.S. Pat. No. 5,071,652 to Jones et al. teaches a metal oxide-hydrogen battery including an outer pressure vessel of circular configuration that contains a plurality of circular cell modules disposed in side-by-side relations. Adjacent cell modules are separated by circular heat transfer members that transfer heat from the cell modules to the outer vessel. Each heat transfer member includes a generally flat body or fin which is disposed between adjacent cell modules. A peripheral flange is located in contact with the inner surface of the pressure vessel. The width of each cell module is greater than the length of the flange so that the flange of each heat transfer member is out of contact with the adjacent heat transfer member. The flanges are constructed and arranged to exert an outward radial force against the pressure vessel. Tie bars serve to clamp the cell modules and heat transfer members together in the form of a stack which is inserted into the pressure vessel.
The metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,071,652 to Jones et al. is designed for cylindrical type of batteries and teaches the heat transfer members in direct contact with the vessel thereby failing to create a clearance between the vessel and the heat transfer members, which can be used to introduce cooling or heating agent to cool or heat the cells.
Referring now to packaging systems of the battery cells, numerous prior art references teach metallic cases used to protect the cells from handling and vibration damage and allowing for combining of multiple cases into a single large pack. However, the metallic cases are expensive to manufacture and each different configuration requires new dies to produce the various components and new tools to assemble those components. Consequently, techniques and materials for enclosing the battery cells in envelopes creating lithium battery cell packs have been developed. Unfortunately, these packages do not provide structural rigidity or protection from handling and vibration nearly as well as the metallic cases, nor can they be combined into consistently sized groups of cells because of the inherent variation in the thickness of a lithium battery cell pack.
There remains an opportunity for an improved battery pack having cell retaining elements to maintain the battery pack at the optimal operating temperature to ensure the longest possible life cycle, with rated capacity, and charge and discharge rates.